Conclusion

Major Points

In ruling out traumatic subarachnoid hemorrhage, the traumatic tap which causes blood to mix with cerebrospinal fluid can complicate the diagnosis of subarachnoid hemorrhage in up to 30% of LPs.[1]

This study was a predefined subsidy of the Canadian subarachnoid hemorrhage (SAH) rule and provides data to classify the likelihood of a subarachnoid hemorrhage based on LP results. Using a threshold of 2000x106/L in the final CSF tube provides for a sensitivity of 100% (CI 74.7-100%) and specificity of 91.2% (88.6-93.3%). For xanthochromia however the sensitivity was only 46.6% (CI 22-72.6%) for diagnosing subarachnoid. Combining the RBC threshold with xanthochromia the sensitivity for subarachnoid hemorrhage is 100%[2]

Study Design

Planned substudy from the prospective multi center cohort study, designed to derive and validate the Ottawa SAH (subarachnoid hemorrhage) rule

Inclusion Criteria

Exclusion Criteria

Recurrent headaches (3 or more with similar character/intensity over 6 month or greater period

Transfered from other hospital with confirmed subarachnoid

Presence of focal neurologic deficits or papilledema

History of

Subarachnoid hemorrhage

Aneurysm

VP shunt

Brain neoplasm

Interventions

Computed tomography and/or lumbar puncture was performed at the discretion of the treating physician

Some LPs were performed before CT scans

Patients discharged without having both computed tomography imaging and a normal result on lumbar puncture were assessed by telephone interview one month and six months after assessment in the emergency department as well as a review of medical records to identify any recorded subarachnoid hemorrhage.

Patients without telephone follow-up or subsequent hospital encounters at the enrolling sites were further checked against the coroner’s records to identify any deaths compatible with subarachnoid hemorrhage

Outcomes

Subarachnoid hemorrhage definition:

Blood in the subarachnoid space on CT brain

Xanthochromia on examination of CSF

Red blood cells in the final tube of CSF fluid and aneurysm shown with cerebral angiography requiring any neurovascular intervention or resulting in death.

Normal LP = 1098
Abnormal LP = 641 (36.9%)

No aneurysmal subarachnoid = 626

Aneurysmal subarachnoid 15

Xanthochromia = 7

No Xanthochromia = 8

Primary Outcome

There were 15 (0.9%) patients with aneurysmal subarachnoid hemorrhage based on abnormal results of a lumbar puncture.

Secondary Outcomes

The presence of less than 2000 × 106/L red blood cells in addition to no xanthochromia excluded the diagnosis of aneurysmal subarachnoid hemorrhage

Criticisms & Further Discussion

Although this study is useful for defining the number of RBCs concerning for a SAH it does not help guide the workup for patients with a negative CT and positive lumbar puncture. There was also a great percentage of patients who underwent CT angiography for a small percentage of SAH.

A study by Gorchynski found that RBC counts ≤ 500 x106/L in the 4th CSF tube had a 100% negative predictive value for subarachnoid hemorrhage[4]

Caution should be used for assessing abscess of SAH based on the percentage drop in RBC count since the presence of SAH was demonstrated in patients with a 25% reduction of RBCs between the 1st and 4th tubes[5]

External Links

Funding

Funded by the Canadian Institutes of Health Research (grants: 67107, 153742), the Ontario Ministry of Health and Long Term Care, and the physicians of Ontario through the Physician’s Services Incorporated Foundation